OAKLAND -- People seeking stiff punishment for Johannes Mehserle plan to gather Friday in downtown Oakland as the former BART police officer is sentenced for killing unarmed train rider Oscar Grant. Police and community leaders expect a smaller turnout than in past Mehserle-related demonstrations, some of which ended with vandalism and arrests. In a letter to the public, City Administrator Dan Lindheim said officials were not urging businesses to close, but instead to "use common-sense precautions and convey a sense of calm."Still, on Thursday, many downtown merchants were boarding up windows. Others had decorated their shops with photos of Grant,...